From: "Toke Høiland-Jørgensen" <toke@redhat•com>
To: Jakub Kicinski <kuba@kernel•org>
Cc: "Marek Majtyka" <alardam@gmail•com>,
"Saeed Mahameed" <saeed@kernel•org>,
"David Ahern" <dsahern@gmail•com>,
"Maciej Fijalkowski" <maciej.fijalkowski@intel•com>,
"John Fastabend" <john.fastabend@gmail•com>,
"Jesper Dangaard Brouer" <jbrouer@redhat•com>,
"Daniel Borkmann" <daniel@iogearbox•net>,
"Maciej Fijalkowski" <maciejromanfijalkowski@gmail•com>,
"Björn Töpel" <bjorn.topel@intel•com>,
"Andrii Nakryiko" <andrii.nakryiko@gmail•com>,
"Jonathan Lemon" <jonathan.lemon@gmail•com>,
"Alexei Starovoitov" <ast@kernel•org>,
"Network Development" <netdev@vger•kernel.org>,
"David S. Miller" <davem@davemloft•net>,
hawk@kernel•org, bpf <bpf@vger•kernel.org>,
intel-wired-lan <intel-wired-lan@lists•osuosl.org>,
"Karlsson, Magnus" <magnus.karlsson@intel•com>,
jeffrey.t.kirsher@intel•com
Subject: Re: [PATCH v2 bpf 1/5] net: ethtool: add xdp properties flag set
Date: Wed, 10 Feb 2021 23:52:39 +0100 [thread overview]
Message-ID: <87czx7r0w8.fsf@toke.dk> (raw)
In-Reply-To: <20210210103135.38921f85@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Jakub Kicinski <kuba@kernel•org> writes:
> On Wed, 10 Feb 2021 11:53:53 +0100 Toke Høiland-Jørgensen wrote:
>> >> I am a bit confused now. Did you mean validation tests of those XDP
>> >> flags, which I am working on or some other validation tests?
>> >> What should these tests verify? Can you please elaborate more on the
>> >> topic, please - just a few sentences how are you see it?
>> >
>> > Conformance tests can be written for all features, whether they have
>> > an explicit capability in the uAPI or not. But for those that do IMO
>> > the tests should be required.
>> >
>> > Let me give you an example. This set adds a bit that says Intel NICs
>> > can do XDP_TX and XDP_REDIRECT, yet we both know of the Tx queue
>> > shenanigans. So can i40e do XDP_REDIRECT or can it not?
>> >
>> > If we have exhaustive conformance tests we can confidently answer that
>> > question. And the answer may not be "yes" or "no", it may actually be
>> > "we need more options because many implementations fall in between".
>> >
>> > I think readable (IOW not written in some insane DSL) tests can also
>> > be useful for users who want to check which features their program /
>> > deployment will require.
>>
>> While I do agree that that kind of conformance test would be great, I
>> don't think it has to hold up this series (the perfect being the enemy
>> of the good, and all that). We have a real problem today that userspace
>> can't tell if a given driver implements, say, XDP_REDIRECT, and so
>> people try to use it and spend days wondering which black hole their
>> packets disappear into. And for things like container migration we need
>> to be able to predict whether a given host supports a feature *before*
>> we start the migration and try to use it.
>
> Unless you have a strong definition of what XDP_REDIRECT means the flag
> itself is not worth much. We're not talking about normal ethtool feature
> flags which are primarily stack-driven, XDP is implemented mostly by
> the driver, each vendor can do their own thing. Maybe I've seen one
> vendor incompatibility too many at my day job to hope for the best...
I'm totally on board with documenting what a feature means. E.g., for
XDP_REDIRECT, whether it's acceptable to fail the redirect in some
situations even when it's active, or if there should always be a
slow-path fallback.
But I disagree that the flag is worthless without it. People are running
into real issues with trying to run XDP_REDIRECT programs on a driver
that doesn't support it at all, and it's incredibly confusing. The
latest example popped up literally yesterday:
https://lore.kernel.org/xdp-newbies/CAM-scZPPeu44FeCPGO=Qz=03CrhhfB1GdJ8FNEpPqP_G27c6mQ@mail.gmail.com/
>> I view the feature flags as a list of features *implemented* by the
>> driver. Which should be pretty static in a given kernel, but may be
>> different than the features currently *enabled* on a given system (due
>> to, e.g., the TX queue stuff).
>
> Hm, maybe I'm not being clear enough. The way XDP_REDIRECT (your
> example) is implemented across drivers differs in a meaningful ways.
> Hence the need for conformance testing. We don't have a golden SW
> standard to fall back on, like we do with HW offloads.
I'm not disagreeing that we need to harmonise what "implementing a
feature" means. Maybe I'm just not sure what you mean by "conformance
testing"? What would that look like, specifically? A script in selftest
that sets up a redirect between two interfaces that we tell people to
run? Or what? How would you catch, say, that issue where if a machine
has more CPUs than the NIC has TXQs things start falling apart?
> Also IDK why those tests are considered such a huge ask. As I said most
> vendors probably already have them, and so I'd guess do good distros.
> So let's work together.
I guess what I'm afraid of is that this will end up delaying or stalling
a fix for a long-standing issue (which is what I consider this series as
shown by the example above). Maybe you can alleviate that by expanding a
bit on what you mean?
-Toke
next prev parent reply other threads:[~2021-02-10 22:54 UTC|newest]
Thread overview: 60+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-04 10:28 [PATCH v2 bpf 0/5] New netdev feature flags for XDP alardam
2020-12-04 10:28 ` [PATCH v2 bpf 1/5] net: ethtool: add xdp properties flag set alardam
2020-12-04 12:18 ` Toke Høiland-Jørgensen
2020-12-04 12:46 ` Maciej Fijalkowski
2020-12-04 15:21 ` Daniel Borkmann
2020-12-04 17:20 ` Toke Høiland-Jørgensen
2020-12-04 22:19 ` Daniel Borkmann
2020-12-07 11:54 ` Jesper Dangaard Brouer
2020-12-07 12:08 ` Toke Høiland-Jørgensen
2020-12-07 12:03 ` Toke Høiland-Jørgensen
2020-12-07 12:54 ` Jesper Dangaard Brouer
2020-12-07 20:52 ` John Fastabend
2020-12-07 22:38 ` Saeed Mahameed
2020-12-07 23:07 ` Maciej Fijalkowski
2020-12-09 6:03 ` John Fastabend
2020-12-09 9:54 ` Maciej Fijalkowski
2020-12-09 11:52 ` Jesper Dangaard Brouer
2020-12-09 15:41 ` David Ahern
2020-12-09 17:15 ` Saeed Mahameed
2020-12-10 3:34 ` David Ahern
2020-12-10 6:48 ` Saeed Mahameed
2020-12-10 15:30 ` David Ahern
2020-12-10 18:58 ` Saeed Mahameed
2021-01-05 11:56 ` Marek Majtyka
2021-02-01 16:16 ` Toke Høiland-Jørgensen
2021-02-02 11:26 ` Marek Majtyka
2021-02-02 12:05 ` Toke Høiland-Jørgensen
2021-02-02 19:34 ` Jakub Kicinski
2021-02-03 12:50 ` Marek Majtyka
2021-02-03 17:02 ` Jakub Kicinski
2021-02-10 10:53 ` Toke Høiland-Jørgensen
2021-02-10 18:31 ` Jakub Kicinski
2021-02-10 22:52 ` Toke Høiland-Jørgensen [this message]
2021-02-12 1:26 ` Jakub Kicinski
2021-02-12 2:05 ` Alexei Starovoitov
2021-02-12 7:02 ` Marek Majtyka
2021-02-16 14:30 ` Toke Høiland-Jørgensen
2020-12-09 15:44 ` David Ahern
2020-12-10 13:32 ` Explaining XDP redirect bulk size design (Was: [PATCH v2 bpf 1/5] net: ethtool: add xdp properties flag set) Jesper Dangaard Brouer
2020-12-10 14:14 ` [Intel-wired-lan] " Magnus Karlsson
2020-12-10 17:30 ` Jesper Dangaard Brouer
2020-12-10 19:20 ` Saeed Mahameed
2020-12-08 1:01 ` [PATCH v2 bpf 1/5] net: ethtool: add xdp properties flag set David Ahern
2020-12-08 8:28 ` Jesper Dangaard Brouer
2020-12-08 11:58 ` Toke Høiland-Jørgensen
2020-12-09 5:50 ` John Fastabend
2020-12-09 10:26 ` Toke Høiland-Jørgensen
2020-12-08 9:00 ` Jesper Dangaard Brouer
2020-12-08 9:42 ` Daniel Borkmann
2020-12-04 12:57 ` Maciej Fijalkowski
2020-12-04 10:28 ` [PATCH v2 bpf 2/5] drivers/net: turn XDP properties on alardam
2020-12-04 12:19 ` Toke Høiland-Jørgensen
2020-12-09 19:05 ` [Intel-wired-lan] " kernel test robot
2020-12-04 10:28 ` [PATCH v2 bpf 3/5] xsk: add usage of xdp properties flags alardam
2020-12-04 10:29 ` [PATCH v2 bpf 4/5] xsk: add check for full support of XDP in bind alardam
2020-12-04 10:29 ` [PATCH v2 bpf 5/5] ethtool: provide xdp info with XDP_PROPERTIES_GET alardam
2020-12-04 17:20 ` [PATCH v2 bpf 0/5] New netdev feature flags for XDP Jakub Kicinski
2020-12-04 17:26 ` Toke Høiland-Jørgensen
2020-12-04 19:22 ` Jakub Kicinski
2020-12-07 12:04 ` Toke Høiland-Jørgensen
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